Acu-Rite KT3D edge finder wiring

I have an Acu-rite KT-3D edge finder I got from my father's shop as he was getting rid of everything. I would like to use it on a CNC router (ShopBot). The way the router works for touching off is you just close a circuit, usually the end mill touches a aluminum touch-plate. I put an ohm meter on the KT-3D to try and figure out how it works, but it's not clear. The wire going into the KT-3D is just one conductor using a mini banana jack. The shaft of the KT-3D is insulated from the rest. I put an ohm meter across the wire and the touch probe tip and it showed about 25 ohms. When I moved the tip, I expected the circuit to open up, but it doesn't; the resistance does go up to a couple hundred ohms, but it fluctuated a lot. If I release the tip to it's neutral position, the resistance does not return to 25 ohms and it still fluctuates a lot. If I remove the test leads for a second and put them back on, the resistance is again around 25 ohms and pretty stable. This has me thinking there's a circuit inside and it's not a simple open/closed connection. Does anyone know the inner workings of the KT-3D?

Attachment 480274

Most of these type probes have small contacts inside. Due to its age they are probably corroded, and need to be cleaned with sandpaper or emery paper. This is just a mechanical switch the resistance with a short cable should be very close to zero ohms. Depending on the electronics involved it could be looking for a higher resistance, but I would be surprised. I would expect a hiZ reading megohms and close to zero when tripped.

Even if the contacts are corroded, it should still show as open when the probe tip is moved. I removed the top section where the 4 screws are, but I can't figure out how to take it apart any further.